The present invention concerns improvements in or relating to systems and devices enabling the monitoring of evolution with respect to the time of logic and analog information data collected from a plurality of points in an information handling and processing equipment and enabling, when necessary, the inspection of sequences of such logic and analog information data for mainly locating faults occurring in the equipment in the course of the time.
Such systems and devices comprise means for permanently recording the information data to be monitored on an endless multi-track magnetic carrier such as a magnetic disc, drum or looped tape. Each track is allotted to a particular point of the equipment from which data is collected. Each track is associated with an erase magnetic head, a writing head positioned just after the erase head or combined therewith, and a reading head. Such means consequently constitute an evolutive information store of a restricted capacity, the content of which progressively changed at each revolution of the looped multiple track recording carrier.
When, in the data handling and processing equipment, an event occurs which may denote a fault or a misoperation, the erase and/or writing heads are inhibited and the reducing heads are activated when they were not already operative. The record is maintained as is without further changes and a repetitive read-out operation of the thus stored data sequences is initiated. To each reading head is associated a visual display means, such for instance as a cathode-ray oscilloscope. When multiple beam cathode ray tubes are used, their number is less than the number of tracks, consequently less than the number of reading heads. The operator can inspect the displays either by mere sight or from graphical records thereof.
During this repetitive display, at least, the X-scan (or the .theta.-scan, as the case may be) of the cathode ray tubes must be synchronized with the passage of the looped record under the reading heads. The synchronization is obtained from a read-out of an index written on an additional track of the record carrier. Each read signal of said index triggers the X (or .theta.) scanning control circuits of the cathode-ray tubes. The index could have been written on its track before the occurrence of the repetitive read-out of the record or at the time the erase and/or writing heads are inhibited.
During at least the repetitive read-out operation, means enable the operator to adjust the X (or .theta.) scanning span on the cathode ray tubes so that he may choose the extent of the field of the record he wishes to inspect from the display. However, as such means do not enable the modification of the origin of the display, since the synchronization track carries a single index, further means are necessary for enabling the operator to control such a modification.
Means for enabling an operator to adjust or modify the origin of the display are provided in French Pat. No. 2,253,439. In this patent, two magnetic heads are associated to the origin index track of the carrier. The upstream head in the direction of movement of the carrier is a reading head, the downstream head in said direction is a writing head. The reading head also is an erasing head (or an erasing head immediately follows the reading head. The output of the reading head is connected to the input of the writing head through an adjustable delay connection so that any index which has been read (and erased) is re-written at a location of the track shifted by such a delay with respect to its preceding location on said track. In this patent there is further described a circuit which ensures the writing of the synchronization index on its track at the time instant of switching of the system from the recording condition to the displaying inspection condition, so that the index initially marks the true origin of the information sequence which remains stored on the carrier.
Actual use of the system described in said French Patent reveals two counterparts or drawbacks. The first drawback is a technological one as it is necessary to physically mount two spaced magnetic heads for the index track. The second drawback and the more important is that, as soon as the inspection begins, at the first change of location of the index on its track, the true origin of the information sequence which is inspected is lost. This loss obviously complicates the interpretation of the display.
It is an object of the invention to provide an improved device which does not present such drawbacks.